Trim the ends and remove the calyx of the okra. Rub with a pinch of salt, rinse under water, and pat dry. Place in a microwave-safe container, cover loosely with plastic wrap, and microwave at 600W for 1 minute. Cool in water, drain, and cut into 1cm slices.

Remove the pit from the umeboshi and mash it into a paste using a knife.

In a bowl, combine the natto, its included sauce, and the umeboshi paste. Add the sliced okra and half the bonito flakes, then mix well.